regulator: da903x: Kill da903x_[get|set]_[ldo12|ldo14]_voltage_sel() functions

Now the implementation of da903x_set_voltage_sel, da9030_set_ldo14_voltage_sel,
and da9034_set_ldo12_voltage_sel are exactly the same.

da903x_get_voltage_sel, da9030_get_ldo14_voltage_sel and
da9034_get_ldo12_voltage_sel are exactly the same.

So we can use da903x_[get|set]_voltage_sel and kill other functions.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>